Field of the Invention and Related art Statement
This invention relates to a track jump controlling apparatus for an optical information recording/reproducing apparatus whereby, in order to access a target track, not only accelerating pulses and decelerating pulses but also additional decelerating pulses can be output by switching a servo on after a fixed time.
Recently there is practiced an optical information recording/reproducing apparatus whereby information can be optically recorded and recorded information can be reproduced by radiating a light spot on an optical recording medium.
Generally, in an optical information recording/reproducing apparatus, many information tracks are concentrically circularly provided on a disc-like recording medium (mentioned also as a disc) so that information may be recorded/reproduced by radiating a minute light spot. A track jump controlling apparatus is provided to move such light spot from the now following track to an adjacent track.
In jumping a track, when a tracking servo is first switched off, accelerating pulses and decelerating pulses are applied to a tracking actuator and the tracking servo is again switched on, the light spot will be pulled by this servo into the nearest track and the jump will end. However, in this method, in the case of making a jump in a disc of a large eccentricity, there will be no guarantee that the speed and deflection at which the light spot reaches the track will have been made small enough to pull the light spot into the target track by the tracking servo and, in some case, the light spot will not reach the target track or will, on the contrary, pass over it. Also, by the fluctuation of the driving sensitivity of the tracking actuator, the same disadvantage will be likely to occur.
Therefore, in the prior art examples of the publications of Japanese Patent Application Laid Open Nos. 109538/1989 and 229473/1989 is disclosed a method of reducing the final speed to be small enough wherein the decelerating pulses are made smaller than the accelerating pulses so that the speed at which the light spot can reach the target track may be left, after it is detected that the light spot has reached the target track (or its vicinity), further the decelerating pulses are additionally output and then the tracking servo is switched on.
In the above mentioned prior art examples, in case there is a large eccentricity, the light spot may not reach the target track. That is to say, unless the light spot reaches the target track, the tracking servo will not be closed and therefore it will fail to pull the light spot into the target track. In order to exclude such case, it is thought that the decelerating pulses must be set to be smaller enough than the accelerating pulses but there have been problems that, if they are so set, when the eccentricity in the direction reverse to the accessing direction to the .target track is large, in case the light spot has reached the target track, it will have a very large relative speed (to the track) and, even if decelerating pulses are additionally output, it will take time to decelerate the pulses, the tracking servo will be likely to be switched on where the light spot has passed over the range in which the tracking servo pulls in the light spot, it will be difficult to stably access the target track and it will take time to access the target track.